1. Field of the Invention
The present invention relates to medical systems in general, and to a method and apparatus for positioning and presenting a device in tubular organs, in particular.
2. Discussion of the Related Art
Interventional cardiology procedures are becoming increasingly important in the treatment of physiological abnormalities such as lumen stenosis or aneurysm. For example, in order to treat a stenotic coronary artery, it is often required to inflate a balloon, apply an atherectomy or thrombectomy device and place a stent (prosthesis) at a diseased artery site. In this example, the devices are either a guide wire or a therapeutic intravascular device, such as a balloon, a stent, an atherectomy, or a thrombectomy device. On the therapeutic stage of the catheterization procedure the physician inserts a guide wire, mounting it distally of the stenotic vessel and then delivers the therapeutic device (balloon or stent) to the stenotic location. In cases of difficult morphology of the vessel the guide wire insertion becomes a challenging task even for skilled physicians. Furthermore, navigation of the guide-wire in anatomies such as bifurcations and branches is always a challenging task. In order to accurately locate the device within the artery, fluoroscopic x-ray images are taken during the navigation of the guide-wire into position. In addition, the subject is often injected with contrast material which facilitates the view of the arteries in the image as well. Real-time assistance in navigation and localization of the guide-wire could prove very helpful in such cases and may reduce contrast material injection. Accurate deployment of the therapeutic device is another important factor of therapy success. It is known that in some of cases, deployment of a therapeutic device such as a stent is not optimal, an indication to that is a necessity to deliver an additional stent to cover the stenotic segment. The issue of the device location becomes even more important when drug-eluting stents are considered. A capability of automatically and accurately locating a device without injecting additional contrast materials, yields certain benefit. The novelty of the proposed navigation system is that it does not require additional equipment beyond the already used guide wire and device. All involved tasks are carried out automatically without altering the standard flow of a catheterization procedure.
Yet another interventional radiology procedure where accurate positioning of a device is crucial for achieving good quality results is a bi-ventricular pacing procedure. By placing a pacing lead in different positions in the coronary vein tree and checking the heart response to the electric impulse, the physician chooses the optimal position and deploys the lead in the chosen position. The problem is to identify each checked location and provide a method of automatic navigation to the chosen one.
In the context of this invention, the term “device” refers interchangeably to a guide wire tip and to a therapeutic device. When the tubular organ is an artery, the therapeutic device is an intravascular therapeutic device, such as a stent or a balloon. The location of a catheter tip, guide wire tip or intravascular therapeutic device with reference to surrounding arterial anatomy is monitored by X-ray fluoroscopy. When necessary, the angiographer releases a contrast material, such as iodine solution, from the catheter tip. The contrast material is carried from the catheter tip by the blood flow, and an X-ray image of the arterial anatomy in the vicinity of the catheter tip is obtained, showing both the artery and the catheter tip. Based upon the obtained X-ray image, the guide wire is advanced until the desired arterial anatomy is reached. Usually, in order to treat the artery, the tip of the guide wire should pass through the diseased region to the distal end of the diseased region. Subsequently, an intravascular device is mounted on the guide wire and brought to the diseased arterial region. Monitoring the location of the therapeutic device inside the artery is performed by following the movement of radio-opaque markers sliding along the guide wire that flanks the device. The markers indicate the position of the device in reference to the guide wire.
Most of the known navigation methods use special equipment for therapeutic device localization. Such equipment can be based on optical or electro magnetic tracking principles using sensors and transducers for measuring position of the device in some reference coordinate system. In order to achieve acceptable results the imaging system and the tracking systems must be well calibrated presenting the image and location of the device in common coordinate system. Additional equipment increases the cost of procedure, makes it more complicated, and requires accurate calibration. Another type of methods for device positioning uses mechanical tools which confine the right positioning for the device. These methods serve specific types of treatments and therefore are not universal. International patent application publication number WO 96/25881 titled METHOD FOR ULTRASOUND GUIDANCE DURING CLINICAL PROCEDURES published on Aug. 29, 1996 describes a method for combining a geometric localization of a tool with acquired ultrasound images. However, ultrasound modality cannot be applied for some organs, such as coronary arteries. WO 96/25881 further describes a method for guiding a tool to reach an organ without intersecting other organs. WO 96/25881 does not relate to navigating a tool located inside a tubular organ towards a pre-defined position within the tubular organ. The target and surrounding organs are required to be visible in images acquired throughout the insertion. Thus, the main difficulty of the registration, which is an essential step in data fusion, is solved by using additional equipment—the organs are imaged by ultrasound throughout the insertion. The last solution is not valid for the case of X-ray angiography, for example.
Another publication demonstrating the usage of Ultrasound technology for real-time imaging of devices, is International patent application publication number WO 01/58359 titled ULTRASONIC IMAGER published on Aug. 16, 2001. WO 01/58359 discloses an ultrasound imaging system that superimposes sectional views created from volumetric ultrasound data, and the location data for an intervention device, such as a catheter as obtained from external sensors. The position of an interventional medical device may be shown, in one or more views, relative to organs and tissues within a body as the interventional device is moved. The interventional device positional data is updated continuously and is superimposed on tissue images that may be updated less frequently, resulting in real-time or near real-time images of the interventional device relative to the tissues. The superimposed images permits medical personnel to perform procedures such as angiograms with minimal or no exposure of patients to x-rays and contrasting dye. The current ultrasound image where catheter appearance is enhanced by vibration mechanism or by brightening technique is supposed to be aligned with a reference image. The combination of the two images is carried out by straightforward overlay. However, as mentioned above, ultrasound technology is not applicable to all organs, and especially to coronary arteries, since the technology does not compensate for changes in imaging conditions and for movement of organs.
U.S. Pat. No. 6,389,104 entitled FLUOROSCOPY BASED 3-D NEURAL NAVIGATION BASED ON 3-D ANGIOGRAPHY RECONSTRUCTION DATA discloses a method for detection of a moving catheter in a lower quality fluoroscopic image and presenting the catheter with high quality 3D reconstructed vascular structure. The suggested method assumes complete information of the imaging perspective geometry both on the diagnostic stage when the 3D model is generated by using images captured by a rotational angiography and on the therapeutic stage of fluoroscopy guided navigation of catheter. Under such restrictive and practically problematic assumptions, one of the central problems of image registration is reduced to essentially carrying out known transformations. Additionally, the suggested method is not applicable to moving organs, such as arteries whose shape changes with the heart beat cycle. Yet another drawback of the method is that the catheter is identified in low quality fluoroscopic images by usage of special intensity modulated catheter. Thus, the method requires complete information of the imaging conditions, a static scene and a special catheter, making it inapplicable for standard coronary angioplasty.
There is therefore a need in the art for a system that will generate a model of a body area including tubular organs, during a diagnostic stage, and will use the generated model for purposes of automatic identification and tracking of a device located inside a tubular organ during a therapeutic stage. It is desirable that the system will use x-ray imaging during the therapeutic stage, although most tubular organs, such as vessels are not visible in x-ray images. The system should not require additional equipment in excess of the equipment currently required for the relevant types of procedures. It is also desirable that the system will perform automatic registration of images between images captured during a diagnostic step and images captured during a therapeutic stage overcoming geometric distortions and differences in content. The system should automatically register the images, determine the location of the device, and will display the device, along with relevant measurement data, together with reference images of the body area or the reconstructed model thereof. The system should minimize the need for harmful contrast material injections and radiations to the subject.